Probability: complement of event?

The probability of a calulator working is 0.96 and therefore the probability of it not working is 1-0.96 = 0.04. The probability of two calculators not working is the product of the two = 0.04*0.04 = 0.016 ~ 0.002. So the probability that she will be able to complete her exam with a working calculator is 1-0.002 = 0.998. So she gains an extra 3.8% which is not an awful lot in this case.